This invention relates generally to impedance matching arrangements and, more particularly, to an arrangement for modifying the impedance characteristics of a transmission line to provide a desired impedance.
In numerous circuit applications, it is essential to provide electrical networks that have a specified input impedance. Impedance matching in transmission systems is a primary concern since a correct match provides maximum power transfer for the transmitted intelligence signal between the various components along the transmission path. An impedance mismatch, for example, between a telephone line and a repeater, will result in a signal loss and produce a reflection of the signal. Reflections in the signal may then produce instability or singing of repeaters in the telephone circuit or may occasion echos which are subjectively objectionable to the telephone user.
Present day telephone transmission facilities present a wide range of impedances since the transmission loop may be of various or mixed gauge construction or may be loaded or non-loaded. Furthermore, the length of the telephone loops vary considerably which has an impact on impedance. A conventional technique for compensating telephone loops with unacceptable impedance levels that connect the central office to the telephone subscriber is by installing a line build-out network in each telephone loop. This type of compensation requires a large number of such networks which are costly and require elaborate and time-consuming installation adjustment by trained personnel. Moreover, since these line build-out networks are adjusted to a specific telephone loop, they are dedicated to that loop. Such networks therefore cannot be utilized within concentrated locations between the switching stages of a central office wherein a smaller number of switched concentrated links and associated build-out networks are able to serve a larger number of telephone subscriber loops.
Accordingly, it is a primary object of this invention to provide impedance matching for bidirectional telephone repeaters that serve telephone subscriber loops so that this apparatus may be utilized in the concentrated links between the switching stages of a telephone central office, thereby substantially reducing the number of telephone repeaters and associated impedance matching networks.